Patent GB-861122-A (GB)
Title: Improvements in or relating to sodium vapour electric discharge lamps
Inventor: FERGUSON HAROLD MATTHEW
IPC: H01J61/74
Filed: 1957-02-22
Abstract: 861,122. Discharge lamps. GENERAL ELECTRIC CO. Ltd. Feb. 24, 1958 [Feb. 22, 1957], No. 6081/57. Class 39(1). A lamp comprising a sodium vapour-rare gas U-shaped discharge envelope contained within an evacuated outer jacket has, within the outer jacket, one or more light-reflecting members separate from the discharge envelope and outer jacket, extending across at least part of the space between the envelope and the jacket, and extending individually or collectively along the major part of the length of the envelope. The discharge envelope and the reflecting member/s can be sealed into an evacuated space within a double-walled outer jacket, the space between the walls of which is also evacuated and sealed. Alternatively, the discharge envelope 1 is sealed into an evacuated single-walled outer jacket 2 and each limb 12 of the envelope is individually provided with a sleeve 13 of transparent heatinsulating material, such as glass, which fits closely round (difference in diameters about 1 mm.) the limb along the whole or the greater part of the length of the limb as described in Specification 801,482. In the construction shown in Figs; 1 and 2 two reflecting members 17 of parabolic or part-circular cross-section are arranged between the sleeves 13 with their concave reflecting surfaces directed outwardly. Each reflecting member 17 can extend along the major part of the length of the limbs or can be formed of a number of shorter members collectively so extending. The reflecting members can be so disposed as to give a symmetric or an asymmetric distribution of light on opposite sides of the plane containing the axes of the limbs 12 of the envelope. The reflecting members 17 are provided, in parts lying on the same side of the plane containing the axes of the limbs 12, with slots or holes 20 which may give an asymmetric distribution of light. The reflecting members can be formed of strips of highly polished sheet aluminium. The reflecting members are supported against transverse movement within the outer jacket by bearing directly against its inner surface. In the construction shown in Figs. 3 and 4 the reflecting members 21, 22 are of approximately V-shaped cross-section and arranged with their apices lying in the plane containing the axes of the limbs 12, the member 21 being located between a limb 12 and the outer jacket 2 and the member 22 between the limbs. The invention can be applied to sodium vapour discharge lamps as described in Specification 826,616 in which the discharge envelope is positioned between two plates of transparent heat-insulating material located one on each side of the plane containing the axes of the limbs of the envelope and each extending over the whole or major part of the length and width of the envelope, a lightreflecting member of approximately V-shaped cross-section being arranged between the outwardly-directed surface of one of the plates and the adjacent part of the outer jacket with its apex directed towards the plate and equidistant from the axes of the two limbs of the envelope. A similar form of light-reflecting member can be employed in a lamp including a single heat-conserving sleeve closely surrounding both limbs of the discharge envelope. The lamps can be mounted within a lantern having light-directing properties for further modifying the light distribution. The envelope filling can be neon containing approximately 0.5% of argon at a total pressure of about 10 mms., with about 1 gr. of sodium. The envelope 1, Figs. 1 and 2, is supported by a spring clip 9 having two spring fingers 10, which clip on to the envelope, and two resilient members 11 which extend into contact with the jacket 2. The sleeves 13 are supported against longitudinal movement by a mica disc 14 which extends across the bore of the jacket 2 and bears against the ends of the sleeves 13. The disc 14 is held in position by a support wire 15 which carries a getter 16. The disc 14 also bears against the ends of the reflecting members 17 to hold their opposite ends in contact with the spring clip 9. In the construction shown in Figs. 3 and 4 the V-shaped reflecting members 21 and 22 are provided at each end with lugs 23 which fit into slots in the mica disc 14 and in a further mica disc 24 located between the sleeves 13 and the spring clip 9. The disc 24 is provided with holes through which the limbs 12 of the envelope project. According to the Provisional Specification one or more light-reflecting members may be formed as coatings on the inner surface of the outer jacket, the coatings being formed by electrodeposition.